This invention relates to a jet pump of novel construction, particularly useful for pumping fluids from an oil well or the like. This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 527,219, filed Nov. 26, 1974, now abandoned. The subject matter of the aforementioned co-pending application is hereby incorporated by reference.
A jet pump is sometimes employed as a submerged pump in an oil well for pumping produced fluids to the surface. Such a jet pump has a suction inlet through which produced fluids, which may include oil, gas, and/or water, are drawn. A high pressure power liquid, which is typically crude oil, is injected through a power liquid jet inlet into a flow passage through the jet pump connecting the production fluid suction inlet and the pump outlet. The power liquid is pumped by high pressure pumps at the ground surface and transmitted to the jet pump by tubing extending down the well to be produced. Momentum of the power liquid injected through the jet inlet is at least partly transferred to the production fluid, thereby raising its velocity head. The mixed fluid from the suction inlet and from the jet inlet passes through a throat having a flow cross section smaller than the flow cross section at the point of injection of the power liquid. Downstream from this throat there is a diffuser section having a gradually increasing flow cross section so that the velocity head of the mixed fluids is converted to pressure head for producing fluids from the well.
A significant problem in the jet pump art is cavitation in the pump. This involves the formation of vapor bubbles in low static pressure regions in the pump followed by collapse of the vapor bubbles as the velocity head is converted to static pressure head in the diffuser. Such cavitation reduces pump efficiency and can lead to severe damage to the pump if it persists. In ordinary jet pumps the power liquid flow rate can be reduced to suppress cavitation. This, however, leads to low production rates and inefficient operation. Alternatively the jet pump can be submerged in liquids in the well on the suction side of the jet pump. This increases the pressure on the suction side of the pump and decreases the tendency to form vapor bubbles when pressure is reduced due to injection of high velocity power liquid. It is often undesirable to submerge a jet pump enough to prevent cavitation since this requires a large column of liquid in the well. This column of liquid can reduce the production rate of fluid from the producing formation, again reducing total production and leading to inefficiency.
It is therefore desirable to provide a jet pump for use in oil wells and the like which is less susceptible to cavitation than conventional jet pumps.